Extend user documentation and mention in EuXFEL's data analysis docs

[philsmt]

Add more exampls, detailed descriptions of what's already builtin and a code reference.

Also, it might be possible to find a place in the data analysis documentation of European XFEL to promote it as a facility-supported tool.

[takluyver]

I guess the Data analysis software page would be the obvious place. Though we might need to think about the sections again - pasha isn't really about either data access or a specific kind of science.